The author mentions Rust's portable SIMD library [0]. The only issue with portable SIMD is it's only available on nightly. I used it in my FFT crate, but we had to switch to the fearless_simd crate in order to get a portable SIMD solution that works on stable [1].
[0] https://doc.rust-lang.org/std/simd/index.html
[1] https://github.com/linebender/fearless_simd